1. Field of the Invention
The invention relates generally to semiconductor devices and particularly to systems and methods of forming interconnect layouts for semiconductor devices.
2. Description of the Related Art
A semiconductor device includes many electronic components, such as transistors, resistors, or diodes, for example. A metallized interconnect layer interconnects the electronic components to form larger circuit components such as gates, cells, memory units, arithmetic units, controllers, or decoders, for example, on the semiconductor device.
To form the interconnect layer, in one implementation, a layer of metal is deposited on the semiconductor device. A photolithographic masking process is then performed to mask off the areas where the metal should remain, according to an interconnect layout. Then, a metal etch is performed to remove the excess metal. This leaves the metallization contacting those areas of the semiconductor device required by design.
To form the mask used in the photolithographic masking process, a photosensitive film is deposited on a layer of hardmask. An optical image of the interconnect layout is transferred to the photoresist by projecting a form of radiation, typically ultraviolet radiation, through the transparent portions of a mask plate or reticule. A photochemical reaction alters the solubility of the regions of the photoresist exposed to the radiation. The photoresist is washed with a solvent known as developer to preferentially remove the regions of higher solubility, followed by curing the remaining regions of the photoresist. Those remaining regions of the photoresist are highly resistant to attack by an etching agent that is capable of removing the hardmask. The portions of the hardmask exposed by the removal of the photoresist are etched away to define the patterned hardmask. Portions of the metal layer exposed by the removal of the hardmask are then etched away to define the metallization interconnect layer.
Semiconductor device designers often desire to increase the level of integration or density of elements within the semiconductor device by reducing the separation distance between neighboring elements, and thus, between interconnect lines.
Unfortunately, the minimum lateral dimension that can be achieved for a patterned photoresist feature is limited by, among other things, the resolution of the optical system used to project the image onto the photoresist. The term “resolution” describes the ability of an optical system to distinguish closely spaced objects.
Processes using pitch multiplication can be used to reduce the minimum printable feature of a photoresist mask, when the mask consists of an array of parallel lines. However, it is difficult to achieve this for metallization masks comprising random shapes. It is also difficult control a constant spacing between the metal nodes of the interconnect layer comprising random shapes since spacers can only be defined around a resist feature.